Fuel injector timing plungers are required to operate under extremely adverse environmental conditions in a fuel injector assembly. Heavy mechanical loads are applied to the timing plunger in both axial and tangential directions. The plunger must reciprocate within a bore in the injector body that is often distorted so the original diametral clearance is not maintained, and the timing plunger is forced against the bore wall during injector operation, resulting in scuffing. Additionally, low quality and contaminated fuels contribute to the creation of an adverse timing plunger operating environment.
The timing plunger material has been modified throughout the years in an effort to make a timing plunger that is both scuff-resistant and wear-resistant and capable of functioning as required under the adverse conditions of the fuel injector environment. However, third body debris interferes with efficient injector function. Third body debris includes particles harder than the plunger or injector body bore which are not intended to be present within the injector. These particles become embedded into the timing plunger surface and ultimately cause the plunger and body to be wedged together so that the plunger cannot reciprocate in the injector body bore and becomes friction welded. The reduction of fuel lubricity, which could be caused by water contamination of the fuel, and may be a characteristic of some alternative fuels, is also a factor contributing to the friction welding of the timing plunger and injector body together. Injector operation is, of course, prevented if this occurs.
The prior art has proposed the use of wear-resistant materials and corrosion-resistant materials to form various structures and components of internal combustion engines. For example, U.S. Pat. Nos. 4,794,894 to Gill and 4,848,286 to Bentz are directed to ceramic tipped pivot rods, and U.S. Pat. No. 4,806,040 to Gill et al. is directed to a ceramic ball and socket joint. U.S. Pat. No. 4,266,729 to Kulke et al. discloses forming an injector valve needle tip and/or disc from a corrosion-resistant material, such as high quality steel, ceramic, or industrial glass. However, neither this are nor any of the prior art of which the inventors are aware addresses the specific problems of fuel injector timing plunger scuffing and sticking which are encountered with available fuel injectors, particularly those used in diesel engines.
The types of fuels increasingly used in diesel engines, particularly fuels with low lubricity, alternative fuels and fuels which may be contaminated with water, require a scuff-resistant fuel injector timing plunger to maintain efficient engine operation. The prior art has failed to provide a fuel injector timing assembly including a timing plunger that is sufficiently scuff-resistant and wear-resistant, particularly when exposed to third body debris and such adverse operating conditions as low lubricity and contaminated fuels to operate efficiently. A need exists for such a fuel injector timing plunger.